The most likely issue is that the credential has expired.
Some alternatives to try:
- Create another credential (personal access token), register that credential in Jenkins, and use it in a test job
- Create an ssh private key, register it with the git provider, register it in Jenkins, and use it in a test job
- Clone the repository from a command line with the username and password embedded in the repository URL to confirm that the username and password are correct
- Create a test job that embeds the username and password in the URL of the repository to confirm the credential is correct